Front Disc Brake
Front Disc Brake
COMPONENT LOCATION
NOTE:
i6 gasoline front disc brake shown; TD4 diesel front disc brake similar.
OVERVIEW
The front brake assembly features a ventilated brake disc and cast-iron sliding caliper with single acting piston.
BRAKE DISC
The brake disc installed to the 3.2 liter i6 gasoline vehicle is 316 x 28 mm (12.44 x 1.10 in) diameter. The brake disc installed to the 2.2 liter TD4 diesel vehicle is 300 x 28 mm (11.81 x 1.10 in) diameter. The brake disc is secured to the wheel knuckle hub with a single screw and is also retained by the 5 wheel securing nuts.
Both types of front brake disc are manufactured with ventilation channels, allowing the disc to achieve high levels of thermal stability even during severe braking.
The disc is cooled as the forward motion of the vehicle draws air through the ventilation channels, and across the surfaces of the disc.
CALIPER ASSEMBLY
The caliper assembly comprises a fixed carrier and sliding caliper. The fixed carrier is mounted to straddle the brake disc and is attached to the wheel knuckle with 2 bolts. The fixed carrier provides the location for 2 brake pads that are mounted on either side of the brake disc, and is formed with guide channels that allow the brake pads to slide toward the disc surface.
NOTE:
The 2 fixed carrier retaining bolts are pre-applied with a thread locking adhesive and must not be re-used during maintenance. New fixed carrier retaining bolts must be used and the original bolts discarded.
The sliding caliper is mounted over the fixed carrier and retains the 2 brake pads within the caliper assembly. The sliding caliper is secured to the fixed carrier with 2 bushed bolts, and is formed with a hydraulic chamber containing a 60 mm (2.36 in) diameter piston and annular seal.
The sliding caliper is connected via a flexible hose to the brake system hydraulic circuit, and also incorporates a bleed screw for maintenance purposes.
The 2 bushed bolts are machined with a smooth surface and are protected from dirt and moisture ingress with a collapsible rubber boot. The bushed bolts allow the sliding caliper limited lateral movement along the fixed carrier.
A housing spring is located on the outer side of the brake disc, and is connected with formed hooks between the fixed carrier and sliding caliper. During operation of the brake, the spring is tensioned as the sliding caliper moves toward the brake disc. The spring assists to move the sliding caliper away from the brake disc as the brake is released.
An anti-squeal shim is installed on the outside edge of each brake pad and reduces Noise, Vibration and Harshness (NVH) from the brake components during operation.
The brake pads are not installed with pad wear sensors.
BRAKE DUST SHIELD
A formed brake dust shield is located between the wheel knuckle and brake disc, and is secured to the knuckle with 3 screws.
The brake dust shield is handed to the relevant side of the vehicle and protects the brake components from cross axle stone throws. The brake dust shield also prevents debris and brake dust from spreading to other parts of the vehicle.
PRINCIPLES OF OPERATION
Brake Application
As the brake pedal is applied, initial hydraulic pressure is felt in the sliding caliper chamber causing the piston to extend toward the brake disc. The moving piston contacts the inner brake pad, forcing the pad along the fixed carrier guide channels and into contact with the inner side of the brake disc.
As the piston extends from the caliper chamber, it passes through an internal annular seal located within the caliper chamber. The movement of the piston distorts the shape of the seal and consequently, the seal applies pressure on the piston outer surface.
The sliding caliper now reacts and commences to slide along the 2 bushed bolts, in the opposite direction to the extending piston. The sliding caliper contacts the outer brake pad, forcing the pad along the fixed carrier guide channels and into contact with the outer side of the brake disc. The housing spring that is attached between the fixed carrier and sliding caliper is tensioned as the sliding caliper moves toward the brake disc.
With both brake pads now in full contact with the brake disc and hydraulic pressure acting on the piston, no further movement of the piston and sliding caliper is possible. The force created by the piston and caliper acting against the brake pads increases rapidly, trapping the brake disc and slowing the vehicle.
Brake Release
As the brake pedal is released, hydraulic pressure in the caliper chamber collapses and force is no longer applied to the brake pads. The brake pads are moved slightly outwards by the action of the rotating brake disc, and the caliper internal annular seal returns to the normal shape. As the seal moves it grips on the piston outer surface and withdraws the piston into the chamber, sufficiently to provide the necessary pad to disc clearance.
This action prevents the piston from holding the inner brake pad against the disc, and also enables the piston to protrude further from the caliper chamber to compensate for brake pad wear.
With no pressure being applied to the hydraulic system, the housing spring tension is also relieved and the spring returns to the normal position. As the housing spring moves, the attached sliding caliper is moved away from the outer side of the disc to provide the necessary clearance between the outer brake pad and the brake disc.